1. Field of the Invention
The present invention relates to a mass spectrometer and a method of mass spectrometry.
2. Discussion of the Prior Art
Mass spectrometers are known which are suitable for performing so called MS/MS experiments wherein in a first step parent ions are mass analysed. In a second step parent ions having a particular mass to charge ratio are selected by a mass filter and are then fragmented in a gas collision cell. The resulting fragment ions are then mass analysed. The mass spectrum of an analyte ion and the mass spectrum of the fragment products of the analyte ion reveal useful information about the structure of the analyte ion and this information may then be used to identify the ion.
It is known to perform MS/MS experiments on triple quadrupole mass spectrometers. Triple quadrupole mass spectrometers comprise a first quadrupole mass filter Q1, followed by a quadrupole ion guide arranged in a gas collision cell Q2. Downstream of the gas collision cell Q2 is provided a second quadrupole mass analyser Q3.
A parent ion mass spectrum may be obtained by setting Q1 to operate in a wide band pass mode (i.e. RF only mode) so that the first quadrupole Q1 operates in non-filtering ion guide mode. The ions then pass through the gas collision cell Q2 but either collision gas is not provided in the collision cell or the energy of the ions passing through the collision cell is arranged to be sufficiently low so that ions are not substantially fragmented within the collision cell. The parent ions are then mass analysed by the second quadrupole mass analyser Q3.
A fragment ion or MS/MS mass spectrum may be obtained by setting the first quadrupole Q1 to operate as a mass filter so that only parent ions having a specific mass to charge ratio are onwardly transmitted by the mass filter. Parent ions transmitted by the mass filter Q1 then enter the collision cell Q2 and are arranged to have an energy such that they fragment upon colliding with gas molecules in the collision cell. The resultant fragment ions are then mass analysed by the second quadrupole mass analyser Q3.
Hybrid mass spectrometers wherein the second quadrupole mass analyser Q3 is replaced with a Time of Flight mass analyser are also known.
It is a feature of both the known triple quadrupole mass spectrometer and hybrid quadrupole-Time of Flight mass spectrometers that two mass filters/analysers are required in order to perform MS/MS experiments.
It is desired to provide an improved mass spectrometer for performing MS/MS experiments.